One of the most frequently recurring problems in the use of computers is the "man-machine interface." That is, how does the user of a computer or other digital system make his wishes known to the system in a form which the system will recognize?
The earliest systems for human input to computers or other digital communications systems (after the early, clumsy, direct binary systems) were based on the familiar typewriter. The Teletype.TM. was used in communications long before the advent of computers, and most early computer systems adopted the Teletype.TM., or a close relative, as a natural input medium, whether to input data directly into a computer or through an intermediate medium such as cards or tape. Today, the keyboard, in one embodiment or another, remains probably the most common mode of data input to computer systems, and to digital data communications systems (i.e. Telex, Tymnet, TWX, etc.) as well. The Bell System's communications program for the deaf is based on the Teletype.TM. or its descendents.
As common as it is, the typewriter is not the most natural of communications media for most people. Training and practice are required to type accurately and well. This is especially intimidating to those with no background in computers. As the use of computers becomes more widespread, however, the need for those unskilled in computer concepts to communicate with computers is growing. It has been recognized for some time by those in the field that some alternate, more natural, method of man-machine communications is needed.
The most natural modes of communication for the majority of people are speech and writing. Obviously, the ideal input mode for many applications would be speech recognition. Although some advances have been made in this field, direct voice input remains impractical at this time. For the deaf, it will never be practical.
It is thus an object of this invention to provide a means for communications with a computer or other digital communications medium through the recognition by the system of a user's handwriting.
Since at least the early 1960's, systems have been available for optical character recognition (OCR) of handprinted characters on documents. One such system is the IBM Model 1287 OCR reader, which is commonly used in such systems as bulk reading of numbers printed on sales slips, utility bills, etc. OCR systems are expensive, complicated, and limited in scope to a small number of handprinted characters (usually numbers) and a slightly larger set of specially designed printed characters (the OCR-A and OCR-B type fonts). They are very sensitive to position of the print on the document and to size and quality of the print. OCR systems are by their nature practical primarily for large batch applications on large, high-speed computer systems. They ae not useful for "real time" on-line communication of data by a user to a computer or data communications system (hereinafter simply "computer").
It is thus a further object of the invention to provide a simple, inexpensive, method of handprinted communications by a user to a computer in "real-time" which is not sensitive to the location or size of the handprinting, and which is not limited to a small character set.
A number of methods of on-line character recognition have been proposed in the past. Most of these systems utilize a special pad or tablet which locates a special pen through the use of a wire grid, ultrasonic reflections, or resistive detection. See, for example, Hall, et. al., U.S. Pat. No. 3,676,848; Donahey, U.S. Pat. No. 3,996,557; Frank, U.S. Pat. No. 3,487,371. Some use templates or overlays to constrain the formation of characters, which must then conform to a special sequence of strokes (Moss, U.S. Pat. No. Re. 30,048), or sense proximity of a pen to a sensing strip, which requires the user to write parallel to, and a specific distance from, the strip (Nassimbene, U.S. Pat. No. 3,182,291). All of the systems using sensing on a special tablet or template restrict the handwriting to that device. The size and/or location of the writing is critical. There may be resolution problems if the spacing between sensing elements of the sensing grid is too large. Alignment of the characters with the grid is critical. Simultaneous data entry onto a manual form or list and into the computer is difficult or impossible, since most of the systems cannot tolerate the interposition of a paper form between tablet and stylus.
It is, therefore, a further object of the invention to provide an on-line handwriting recognition system which is independent of the medium being written upon, which does not require any special tablet or template, and which is, with broad limits, insensitive to size and orientation of the characters written.
In search of such a system, several inventors have previously devised tablet independent devices. For examples, see Nolf, U.S. Pat. No. 4,241,409; Crane, et al., U.S. Pat. Nos. 3,930,229 and 3,145,367; Narayanan, U.S. Pat. No. 3,835,453; and Gaffney et al., U.S. Pat. No. 3,199,078. Each of these shows a stylus capable of detection of a plurality (usually 4) of directions. As each of these inventors has realized, handwritten characters can be recognized by looking at the directions the stylus has traveled between being placed on the paper ("pen down") and being lifted at the end of a character or segment ("pen up"). Ignoring the distance the pen moves allows the system to be independent of character size.
These systems generally comprise a moving contact attached to the pen point which can touch any one of a number of contacts (usually 4) to indicate which direction the pen is traveling. The sequence of directions is stored and compared to a table to determine the character written. Typically, a "tree" structure, as shown in Crane, U.S. Pat. No. 3,930,229, is used, or the exact list of directions is compared to a table, as in Crane, U.S. Pat. No. 3,145,367. A circuit, often a read-only-memory type device, is set up to recognize a set of characters, which must be written in the predetermined way.
Experimentation has shown that each of these systems has several major problems in practical use. The most important of these is that in each of these systems the stylus indicator is free to move from any direction to any other direction, a condition I term "open loop". That is, in the four direction systems used (up, down, left, right), each may generate a string such as "up, left, right" as a valid string (see Crane, U.S. Pat. No. 3,145,367, "4" in FIG. 4). In theory, this will work. In practice, however, the pen will tend to wiggle from direction to direction as the user writes, causing a large number of random errors to be introduced into the string. Even a single introduced error in direction will cause the sytem to fail. When more than four directions are sensed, this failure of the "open loop" system becomes even more pronounced.
I have found that four-direction sensing is wholly inadequate for full alphanumeric character recognition. The resolution is not accurate enough to allow flexibility in formation of characters, which is a very important object of my invention. As an example, FIG. 4 of Crane, U.S. Pat. No. 3,145,367, shows a chart giving the codes generated using a four-direction detector. As can be seen, Crane's detector cannot distinguish an "A" from a "1" unless the letter is crossed from right to left, a very unnatural way of writing. The optimum resolution I have found is eight directions, although, in an English system "northwest" could be combined with "north", and seven direction resolution would suffice. Using the preferred eight-direction sensing the "open loop" detectors become effectively useless. The random direction "noise" caused by "wiggling" of the pen obscures the characters to be detected.
In addition to the detector problems, the recognition systems described in the prior art suffer from large storage requirements (three to four "bits" per direction, using eight direction resolution) and inflexibility of character formation.
It is an object of this invention to provide a character recognition system which can use a minimum of storage, and allow a maximum of flexibility in character formation.